3.16 : Visual Agnosia

Visual agnosia is a condition characterized by the inability to recognize visually presented objects despite having normal vision. For instance, a person with visual agnosia can describe the shape and color of an object but cannot identify or name it. This impairment does not affect their visual field, acuity, color vision, brightness discrimination, language, or memory. An example of this condition in a social setting is someone at a dinner party asking for "that silver thing with a round end" instead of "the serving spoon."

Visual agnosia can be classified into two subtypes: apperceptive visual agnosia and associative visual agnosia. Individuals with apperceptive visual agnosia often have difficulty recognizing objects, drawing, or copying figures accurately. They are unable to perceive the correct forms of objects, even though their knowledge of the objects remains intact. For example, they might see a series of lines and shapes but fail to recognize it as a drawing of a house.

On the other hand, those with associative visual agnosia can draw or copy objects but cannot identify what they have drawn. They perceive the form of the object correctly and can recognize it when given verbal or tactile information. However, they cannot link the fully perceived visual image to previous experiences to help them recognize the object. For instance, they might draw a picture of a bicycle accurately but be unable to identify it as a bicycle afterward.